Within the telecommunication switching field, it is not uncommon to have two switching systems physically located together and to have a first switching system being synchronized to one of a set of external links that terminate on the second switching system. In the prior art, this has been accomplished by hard wiring each of the set of external links to a central timing unit of the second system. Normally, the central timing unit would use another one of the set of external links to generate the internal timing for the second system. The central timing unit needed a first synchronizer to generate the internal timing and a second synchronizer to generate the timing for the first system. Both synchronizers had to have the capability of selecting any of the set of the external links. In addition, a separate internal physical link had to be connected from each port circuit terminating each of the set links to the central timing unit. Since any external link could be included in the set of external links, each port circuit had to have a physical jack to allow the connection of the port circuit to the central timing unit. In a large system in which the port circuits where distributed over a large area, it was difficult to maintain good transmission characteristics on the internal links over large distances. Also, it was difficult to perform software maintenance operations on the individual internal links.